Thursday, September 13, 2012

About that paper on organic food...

A good biology paper will make you think about life; a few
of them make you think about your own life.A research paper came out this week that made a bit of a splash, and
prompted a lot of people—a lot of non-scientists, who may not be used to
thinking scientifically—about what they are doing and why.The paper was a meta-review: essentially, an
attempt to compare lots of different studies, with different methodologies,
different foci, and different motivations, and reach a coherent
conclusion.The question that the
authors were trying to answer is in the title of their paper: “Are Organic
Foods Safer or Healthier Than Conventional Alternatives?”

The answer is very, very close to “no,” followed by some asterisks.Some of the asterisks are whether the government
approved levels of pesticides are actually safe, and that while the levels of
bacterial contamination were comparable, the contaminants in conventional foods
were more likely to be antibiotic resistant.But on the whole, no difference.

Looking at NPR and the NY Times blogs and their commenters,
a few have their faith shaken by facts, but most have their faith reinforced by
being liberated from facts.They turn to
attacks on the paper and its authors.There’s also a fair amount of triumphal crowing from folks who (like my
dad, a biochemist) refuse to buy organic on principle.

So, as a person who tends to buy organic and pay attention
to science, what do I think?I think I’m
going to have a heart attack and die of not surprise.Whether produce is good and good for you or
not—as long as it falls within guidelines for pesticides and other
contaminants—is a matter of whether the farmer was competent and the food has
gotten from farm to you in a timely and careful fashion.So, why do I tend organic?

I’ll set aside human reasons, although conventional ag
inevitably causes worker exposure to nasty chemicals, which is a good reason to
favor organic.I’ll set aside whether
there is any safe level of pesticides in food, because there isn’t yet any
scientific agreement on the subject.I’ll
also set aside (for now) the effects of using huge amounts of antibiotics that
can leak into the environment.Instead,
I’ll (predictably) focus on microbes, since they make the world go ‘round and
are more important than people in the long run.

I love long-term studies (I mean, what is our planet but a
long term environmental study?).The
Swiss government started just such a study in 1978, comparing three variations
on farming for typical Swiss crops:conventional agriculture with pesticides, herbicides, and chemical
fertilizer supplemented with animal manure, organic farming with no herbicides
or pesticides and only animal or plant manures, and “biodynamic” farming.They did not address which produce is better
for you, or which tastes better; they’re Swiss, so the conventional stuff was
within pretty tight government regulations, and they’re scientists, so all the
crops were equally fussed-over.What
they did compare was the performance of the farms as if they were factories,
and the health of the farms over the course of decades.(Just to simplify things, I’m lumping
together the results of biodynamic and organic practices, since they were
essentially the same.)

I’ll start with the result my dad would point out:yields in the organic fields just weren’t as
high as in the conventional fields.Potatoes, beets, barley, wheat, it didn’t matter, yields from the
organic fields rarely equaled those from the conventional fields, and were
generally about 80% of the conventional yields.This is not a trivial point in a world that’s trying to feed 7 billion
people with limited amounts of cropland and ever-more-difficult access to
water.

However, there are other factors that are limiting, and
energy is right up there.Comparison of
the energy inputs to get those crop outputs is illuminating.The researchers figured out how much energy
was needed for farming activities such as tilling, and added the substantial
energy for making mineral fertilizers, nitrogen, pesticides, and herbicides.Over a six-year period, they discovered that organic
farming took slightly more than half as much energy per hectare, so even though
yields per acre were slightly reduced, organic farming was still vastly more
efficient.(I’ll also note that about
when this study was published, my dad abandoned his SUV for a Prius.)

Soil is the factory that produces food.Clearly, organically farmed soil is a
different kind of factory from conventionally farmed soil—more efficient with
energy, though less efficient with space.It’s the architecture and the workers in the factory, and how they
interact and affect each other, that make the difference.

In this study, there is a visible difference between organic
and conventional soils.

In this picture of winter wheat seedlings, the
biodynamically farmed soil shows more weeds, but the soil looks friable and there
are plenty of worm casts. These
differences are quantifiable; water drainage is improved, as well as the
ability of the soil to cohere.

The workers in the factory of soil are microbes and small
invertebrates.It’s not too surprising
that organically and biodynamically farmed soil has a lot more life in it—the
Swiss study found twice as many earthworms, spiders, and beetles, and much more
root-associated fungi.The sheer mass of
microbes was higher, as was both their genetic diversity and (as has been found
in similar studies) their enzymatic and metabolic diversity.We are constantly told that a more diverse
workplace is better, and at least in the work done in the soil, this seems to
be the case.To really understand this,
though, we need to see what these workers do.

We might think of plants as rugged individualists, gamely
taking sunlight and water and CO2 and pulling themselves up by their
own bootstraps.In reality, they depend
upon soil microbes, both bacteria and fungi, for making many (or most) of their
nutrients available and delivering them to their roots.These microbes break down the components of
wood so that the elements therein can be absorbed by plants; they convert
chemically inert atmospheric nitrogen into a form that the plant can absorb;
symbiotic fungi called mycorrhizae, which grow both in soil and extend their
threads into the cells of plant roots, capture these liberated nutrients and
inject them directly into the plants.All the players in this system, plants, fungi, and bacteria, have
evolved to work with each other, and all fail to thrive in the absence of the
others.A plant is a visible expression
of the health of the soil community.

The Swiss study, as well as studies on Italian rice, Dutch
onions, California strawberries, and other combinations of crop and soil, have
found that the diversity of the soils microbes and mycorrhizae are higher in
organic soils.(Indeed, as soils go, the
champions are wild, uncultivated soils, with many different types of plants growing
in them—but that’s not agriculture.)These
soils show increased ability to break down manure, an increased ability to
mobilize nutrients such as nitrogen and phosphorus, and increased interaction
between mycorrhizae and plant roots.

When the Swiss researchers examined conventionally farmed
soil, they found limited microbial diversity, and reduced metabolic diversity
(that is, the number of different types of biological reactions
occurring).However, they found
increased metabolic activity (that is, the amount of microbial nutrient
consumption aimed at just making energy to live, as measured by the amount of
CO2 the microbes exhaled).In the simplified environment of conventional
soil, the microbes had to work harder to do less. This is not a fluke; a similar observation was
made in comparing organic and conventional strawberry fields in California.

This illuminates the gross productivity and efficiency
differences seen between the conventional and organic systems in the Swiss
study.The conventional soils had
greater yield, but (because they are less efficient factories) they required
much higher inputs of material and energy.Organically farmed soils are healthier.Arguing for conventional farming because arable land is a scarce
resource ignores the fact that, unless there is a large input of energy and
skill, conventional farming can result in the degradation and loss of that same
scarce resource

Of course, factories have more than one product; even the
most efficient factory will produce some waste.Even here, organic farming has some benefits, and these benefits also
are a result of the more diverse and efficient microbial community in
organically-farmed soils.

The job of any factory is to convert raw materials into a
mix of useful products and waste, hopefully with an emphasis on the
former.Farmers, whether organic or
conventional, add raw materials to their soil factory, and they are
particularly mindful of the nitrogen they add.Organic farmers add various forms of manure for their nitrogen content—chicken
or cow wastes, or composted legumes.Conventional farmers will supplement or replace these nitrogen sources
with calcium nitrate or anhydrous ammonia (as an aside—production of this
fertilizer consumes upwards of 1% of the global human energy budget).This is the raw material that enters the
factory; some of the nitrogen gets incorporated into the plants, but a lot of
it will disappear as waste.And here is
where there is a significant difference between conventional and organic soils,
again due to their microbial composition.

Nitrogen compounds are neat.Most of the earth’s nitrogen is in the form of nitrogen gas (N2)
in our atmosphere; this is inert, so chemically unreactive that it is used to
protect precious documents and Guiness beer.A few microbes have learned how to “fix” this atmospheric nitrogen, to
make ammonia (NH3), which is like rocket fuel for plant growth.Lots of soil microbes love to eat ammonia
too, but rather than using it for growth, they oxidize it for energy; in the
process called nitrification, they take ammonia and make it into nitrate (NO3-).Nitrate is a mixed blessing; plants can use
it, though not nearly as well as ammonia.Mostly it leaches out of the soil and pollutes waterways, leading to
algal blooms and their resultant die-offs and dead zones.Microbes can also take nitrate in the soil
and use it for respiration the same way we use oxygen, in a process called
denitrification.Some denitrifiers convert
the nitrate into nitrous oxide (N2O), which disappears from the soil
as a gas; it’s not a good thing, given that it can degrade ozone and is also,
gram for gram, about 300 times more effective as a “greenhouse gas” than carbon
dioxide.Other denitrifiers use the
nitrate more effectively, and convert it back to nitrogen gas.

Either way, as a result of this nitrogen cycle, a farmer can
add nitrogen to the soil and watch some of it disappear as waste; it’s just a
matter of whether the added nitrogen disappears by leaching (and polluting the
water) as nitrate, by going into the atmosphere as pollution in the form of
nitrous oxide, or by going into the atmosphere as benign nitrogen.Since the nitrogen cycle is largely driven
by microbes, and since organic and conventional farming techniques result in
different soil microbiota, it seems like a reasonable hypothesis the way
nitrogen leaves the soil would differ in organic and conventional situations.

No matter what form of agriculture, human activity dominates
the addition of nitrogen to the soil.Conventional farmers add over 80 million metric tons of ammonia to the
soil every year, and organic farmers add manure.This, combined with using legumes in crop rotation,
determines the start of the nitrogen cycle.However, according to a study comparing organic and conventional apple
orchards in Washington state, the fate of the nitrogen differs significantly.

In the organically fertilized orchard, nitrogen was added in
the form of manure; the soil microbiota broke down the manure, so nitrogen
entered the soil more slowly, making it easier to be assimilated.Of the nitrogen that was not used by the
trees and left the soil, only 10% leached out as nitrate.Because of the denitrifying microbes in the
soil, 10% was denitrified to N2O, and 80% was denitrified to
harmless nitrogen gas.

In the conventional orchard, nitrogen was added in the form
of calcium nitrate, a common agricultural fertilizer.The same amount of nitrogen was added, and
the trees grew as well, with the same amount of nitrogen in their leaves and a
comparable amount of nitrogen leaving the orchard as waste.Here, only 20% of the nitrogen left by
microbial denitrification, half as N2O and half as nitrogen
gas.The remaining 80% of the added
nitrogen left by leaching out of the soil as harmful nitrate.There is a striking correlation between the
richer microbiota of the organic orchard and the increased ability of the soil
to process nitrogen into environmentally benign forms—with, as the authors of
this study note, no effect on the yield of fruit.

Which brings us back to the whole question of whether or not
to go organic, and thanks to the news-making review, we can ignore questions of
nutrition. Those who argue against
organics point to increased cost, and less efficient use of land.I think that some of the costs of
conventional agriculture are distributed or hidden—increased energy inputs per
acre, and the costs of dealing with increased pollution.Land use may be less efficient in the short
term, but unless there is active and conscientious management of conventional
soils (another hidden cost), organic soils are healthier and more
sustainable.

The goal is aspirational; right now, organic stuff is more
expensive, and that’s a hardship for some.Many farmers (not to mention some pretty enormous agribusinesses) are
pretty set against organic growing.There’s also situations that are really difficult to address with
anything but conventional means.I am an
example; I am using Crossbow to clean up blackberries and poison oak and vinca that
have accumulated after several years of neglect.But, the goal here is a transition to
organic, and it is doable and right.

So, imagine I offered you a couple of MP3 players for sale;
they are functionally identical, and both will fill your ears and satisfy your
musical desires.However, one costs 20%
more than the other.What’s the
difference?One is made in a
coal-powered factory that produces a large amount of toxic wastes and causes
damage to its local environment, while the more expensive one is from a
renewably-powered factory that actually collects and recycles waste, cleaning
its environment.Which would you choose?

Galván, Guillermo A., István Parádi, Karin Burger, Jacqueline Baar,Thomas W. Kuyper, Olga E. Scholten, and Chris
Kik (2009).Molecular diversity of arbuscular
mycorrhizal fungi in onion roots from organic and conventional farming systems
in the Netherlands.Mycorrhiza19(5):
317-328. Onions, with their weak roots, are quite dependent upon mycorrhizae; since the farms were in polders, the soils were very new to agriculture, but even so, mycorrhizae were present.